The present invention is directed to constructions of ball grid array (BGA) packages having heat sinks and to methods for removing those packages from printed circuit boards or motherboards for repair or replacement.
A BGA is a packaged integrated circuit in which one or more integrated circuit chips (semiconductor dies on which electrically conductive circuitry are formed) are mounted on a (top) surface of a substrate, and an electrical connection to electrically conductive material not part of the packaged integrated circuit, such as a printed circuit board, is made by an array of solder balls located on a (bottom) surface of the substrate opposite the surface to which the integrated circuit chip or chips are attached. Passive components such as resistors or capacitors can also be mounted on the top surface of the substrate. The substrate can be a multi-layer substrate, electrically conductive traces and/or regions being formed on a surface of each layer of the substrate. The integrated circuit chip or chips and the passive components are typically encapsulated by, for instance, plastic to protect them from the external environment. The integrated circuit chip or chips are electrically connected to the substrate by wire bonding or by tape-automated bonding (TAB), or flip-chip interconnection. BGAs allow a higher density of external chip connections to be made than do other packaged integrated circuits having leads extending from the package. An example of a BGA package is shown in U.S. Pat. No. 5,355,283 (Marrs, et al.).
Heat is inevitably generated during the operation of integrated circuit devices, such as BGAs. In some instances, the amount of heat generated can be sufficient to irreparably damage or even destroy the device. Continuing advances in the number of transistors and other functional elements contained in a single integrated circuit, and the increasingly high speeds at which integrated circuits now operate, both contribute to the problem of integrated circuit heat dissipation. The heat can be so great that some devices require that a powered fan be incorporated on them to prevent their failure; an example is the Pentium chip available from Intel Corp. and which is sometimes sold with a small fan mounted on the component itself.
It is generally well known to provide some sort of heat sink for semiconductor devices to remove and dissipate the heat. A variety of methods and devices have been developed for removing at least some of the heat from integrated circuit devices. Typically a unitary heat sink structure has been used. Heat sinks generally include at least a heat-transferring portion proximate to the semiconductor device for extracting heat therefrom, and a heat-dissipating portion remote from the die with a large surface area for dissipating heat. The heat-dissipating portion is typically formed with a number of parallel layers, through which air passes to remove heat from the heat sink. Typically, the entire heat sink structure may simply be disposed on an exterior of a package, such as on the lid of a lidded package.
The heat sinks are typically attached to the package with epoxy. However, this renders them vulnerable to being impacted and torn away. Also, they cannot be easily removed from the package. Additionally, when attached, repair stations cannot be fitted over them to allow hot nitrogen gas to reflow the solder balls. This prevents defective packages from being removed from motherboards for repair or replacement.
Other types of heat sink securements are known, as shown in U.S. Pat. Nos. 5,227,663 (Patil, et al.) and 5,293,930 (Pitasi). A further example is a threaded heat sink attachment available from Vemaline Products of Warwick, Rhode Island. This attachment provides that the heat sink is threaded into a small clip-on device. This device is made of plastic and is clipped over the sides of the printed circuit board. However, this device does not work well, since it falls off easily.